Coating apparatus

ABSTRACT

Aluminum or other coating material is deposited on the surface of one side of a strip after which ink is deposited on preselected areas of the coated strip. The ink is then cured and the aluminum removed from the uncovered areas after which the ink is removed from the covered area of the aluminum.

This invention relates to an apparatus for depositing a coating materialon preselected areas of a substrate and more particularly for depositingaluminum on lead frame strips for the electronic industry. The two mostcommon methods of doing this are by masking all the strip except theportion on which aluminum is desired by means of masking wheels asdisclosed in Krumme et al U.S. Pat. No. 3,735,728 dated May 29, 1973;and by depositing aluminum over the entire surface of the strip, thenmasking with tape the surface on which aluminum is desired, after whichthe aluminum is removed from the unmasked areas. The tape is thenremoved. Both of these methods have the drawbacks that the size andlocation of the stripe or other aluminum covered area are dependent uponmechanical tolerances in machine set up and do not lend themselves tofast rates of production. Processing and tooling costs are high. In U.S.Pat. No. 3,735,728 the entire process must be carried out in a vacuum sothat both mask and parts must be indexed in the vacuum. Long start-upand shut-down times are required.

St. Clair et al U.S. Pat. No. 3,537,175 dated Nov. 3, 1970 discloses amethod and apparatus which is the best art of which I have knowledge. Inthis patent the strip is coated with aluminum in a vacuum depositionchamber and the material is then stamped into lead frames. To obtain thedesired aluminum configuration on the stamped parts they are selectivelyetched to leave the desired pattern. The selective spot is put on bypassing the strip of stamped parts between a masked strip and a rotatingwheel. A plastic material is sprayed on to the exposed portions of thestamped strip and then dried. Then the strip is run through a causticsoda solution to etch the uncovered aluminum after which the plastic isremoved by acetone solutions. This arrangement has severaldisadvantages. It is necessary to use a sprayed mask for selectivelycoating the stamped parts with the plastic resist. Also, the plasticspray accumulates on the mask as well as on the drum over which the maskand strip pass. The amount of heat required to speed up the drying is sohigh as to cause many problems. The plastic spray contains a largeamount of moisture and since it is slow drying the speed of the line islow.

I have found that by using ink and applying it be means of rolls, notonly is maintenance less, but a more accurate ink design is applied at amuch greater speed.

It is therefore an object of my invention to provide an apparatus fordepositing a coating material on preselected areas of a substrate whichis less expensive and faster than in prior systems.

Another object is to provide such an apparatus which does not require aseparate mask and/or a slow drying plastic spray or the use of a tapesystem.

Still another object is to provide apparatus for depositing a coatingmaterial on preselected areas of a substrate which is less expensivethan those of the prior art.

A further object is to provide such apparatus in which the partsfollowing the initial coating are located out of a vacuum.

A still further object is to provide such apparatus which can operatefaster than those of the prior art.

These and other objects will be more apparent after referring to thefollowing specification and attached drawings in which;

FIG. 1 is a schematic view of an aluminum vapor deposition line used inmy invention;

FIG. 2 is a schematic view of the ink deposition line of my invention;

FIG. 3 is a schematic view of a line for selectively removing aluminumand ink according to my invention;

FIG. 4 is an elevation of a rotogravure wheel used with my invention;

FIG. 5 is a sectional view of the striping roll of FIG. 2;

FIG. 6 is a plan view of the workpiece coated on the apparatus of FIGS.1 to 5;

FIG. 7 is a schematic view of a modified ink deposition line;

FIG. 8 is an elevation of the dotting roll of FIG. 7;

FIG. 9 is a view taken on line IX--IX of FIG. 8; and

FIG. 10 is a plan view of the workpiece coated on the apparatus of FIGS.7 to 9.

Referring more particularly to FIG. 1 of the drawings reference numeral2 indicates a reel strip S is unreeled and fed through a conventionalaluminum vapor deposition line 3 such as shown in the St. Clair et alpatent. Here one side of the strip S is coated with aluminum and thecoated strip is coiled onto reel 4. The reel of coated strip S is thenfed from a reel 6 (FIG. 2) around rolls 8, 10 and 12 supported inframework 14. The rolls 8, 10 and 12 have flat bottomed grooves 16, 18and 20 of just sufficient width for receiving the strip S. The groove 18in control guide roll 10 is very accurately machined so that the strip Sis precisely positioned. Also positioned in frame work 14 is a reservoir22 for receiving ink 24. The reservoir is movable vertically in order toenable ready replacement and removal of an inking wheel 26 which is aplain rotatable rubber covered roll. A rotogravure wheel 28 bearsagainst wheel 26 and also against a striping roll 30 which in turn bearsagainst roll 10. Wiper blades 32 and 34 are provided for wheels 26 and28, respectively. The wheel 28 has spaced apart small cavities 36 in itsouter surface and roll 30 has a rubber outer rim 38 having a peripheralprojection 40. From roll 12 the strip passes through a box 42 having anultraviolet light 44 therein after which it is coiled on a reel 46. Thestrip then passes from a reel 48 (FIG. 3) successively through a spotweld station 50, an aluminum etch tank 52, a water rinse tank 54, an airdrying compartment 56, a methylene chloride tank 58, a water rinse tank60, and air drying station 62 to a reel 64.

The operation of my device is as follows when the strip S is made of alow expansion alloy on which an aluminum stripe SS is to be applied withthe strip being used for integrated circuit lead frames. Ink 24 isplaced in reservoir 22 with wheel 26 in contact therewith. A suitableink is SR-12 manufactured by Dyna-Chem Corporation, which is over 90%solids, but this vary depending upon the substrate and coatingmaterials. Aluminum is applied to strip S in the vapor deposition line 3and coated strip from reel 6 is then passed through the ink applicatorline to reel 46. The rotating inking wheel 26 picks up ink from thereservoir 22 and feeds it to rotating wheel 28 where it is received inthe cavities 36. The wipers 32 and 34 remove excess ink from the wheels26 and 28. Ink from wheel 28 is fed onto peripheral projection 40 ofroll 30 which in turn places a stripe SS of the desired width on thestrip S. The ink on the strip is then dried or cured as it passes underultraviolet light 44 after which it is coiled on reel 46. The strip isthen fed from reel 48 to tank 52 where the uncovered aluminum is removedby sodium hydroxide or other suitable agent. The strip is then rinsedand air dried before passing into the methylene chloride tank 58 wherethe ink is removed. The strip is then dried and coiled on reel 64 whereit is ready for use. When one reel is exhausted the leading end of stripon a second reel is welded to the end of the strip of the first reel atstation 50. While the aluminum coating line, ink applying line and theremoval line could be interconnected, I prefer not to do this since themost efficient speeds of the lines are different. Ink one ink applyingline the speed is 260 ft. per min. and a faster line is being designed.This compares to a maximum speed of about 30 ft. per min. for a linesuch as shown in the St. Clair et al patent. This difference is due tothe time required to apply and cure the plastic material.

Other coatings may be applied to other substrates and the design of thecoating may be varied in some cases by merely changing the configurationof wheel 10. In other cases the strip must be indexed. FIG. 7 shows amodified ink applicator line for this purpose when coating resist spotsS'R on a stamped lead frame strip S'. It will be seen that this strip(FIG. 10) has spaced holes S'H along each side. In this embodiment thealuminum coated strip S' passes around guide roll 8' to guide roll 12'.Between the guide rolls a rubber cover pressure roll 70 deflects thestrip S' into contact with a dotting roll 72. The dotting roll 72 haspins 74 spaced around its periphery with the size and spacing of thepins such that will engage holes S'H. the dotting roll also includesrubber projections 76 of such size and spacing that will apply ink onstrip S' at spots S'R. In this embodiment the striping roll 30 isomitted and the ink is applied from wheel 28' directly to wheel 72. Noseparate line is required for this purpose. If strips S and S' are thesame width the rolls 8', 12' and wheels 26' and 28' will be rolls 8 and12 and wheels 26 and 28 of the first embodiment with roll 30 beingremoved and wheel 28 being positioned to bear against roll 72 whichreplaces roll 10. Roll 70 will obviously be inoperative when the line isused as in the first embodiment. For different width strips, rolls ofdifference widths will be used. The coating and coat removal lines willbe as in the first embodiment.

While two embodiments have been shown and described, it will be readilyapparent to those skilled in the art that various adaptations andmodifications may be made within the scope of the invention.

I claim:
 1. Apparatus for depositing a coating material on preselectedareas of an elongated strip which in a continuous system comprisescoating material depositing means, means for passing said strip throughsaid coating material depositing means to deposit coating material onthe surface of one side of said strip, ink depositing means, means forpassing said strip with said coating thereon through said ink depositingmeans to deposit ink only on said preselected areas, ink curing means,means for passing said strip with ink deposited thereon through said inkcuring means to cure said deposited ink, strip etching means, means forpassing said strip with said cured ink thereon through said stripetching means to remove coating material from that portion of the stripnot covered by said cured ink, ink removing means, and means for passingsaid strip from said strip etching means through said ink removing meansto remove the ink therefrom, said ink depositing means including areservoir having said ink therein, an inking wheel above and extendingdownwardly into said ink and a rotagravure wheel having its periphery incontact with said inking wheel and with an applicator roll and saidapplicator roll having a peripheral groove of slightly larger width thansaid strip, indexing projections adapted to operatively associate withindexing holes in said strip and coating projections corresponding tosaid preselected areas on said strip.